Lymph is a generally transparent, slightly yellow fluid substance which comprises a clear liquid and cellular components, such as lymphocytes. In recent years, it has been shown that lymphocyte depletion by thoracic duct drainage has immumosuppressive effects which can be useful in preventing rejection of transplanted tissue and the treatment of auto-immune diseases.
In the past, lymphocyte depletion has been accomplished by removing lymph from a patient and replacing that lymph with a solution of 5% albumin in saline (plasmetin) mixed with fresh plasma. Lymph has also been withdrawn from a patient, frozen and held for 6 to 7 days to kill the lymphocytes, and then thawed and returned to the patient. Another method removes lymph from a patient, centrifuges it and then returns the liquid fraction to the patient, discarding the cellular component fraction. However this takes extensive equipment and is difficult to use for continuous separation. Filtering is effective for continuous separation except that the filter eventually becomes clogged or plugged with cells and debris.
Various designs have been proposed for devices to separate a body fluid such as blood into a cellular component fraction and a liquid fraction. Illustrative of such devices are U.S. Pat. No. 4,111,199 to Djerassi, U.S. Pat. Nos. 4,059,108 and 4,086,924 to Latham, U.S. Pat. No. 4,083,786 to Tsuda et al., U.S. Pat. No. 3,705,100 to Blatt et al. and U.S. Pat. No. 4,191,182 to Popovich et al. However, none of these devices are directed to a treatment of lymph. The devices to Popovich, Djerassi, Latham and Blatt all are designed to return the cellular component fraction to the patient and are not suitable for lymphocyte depletion which disposes of the cellular components. None of these devices disclose a means to maintain a filter element in an operating condition without becoming plugged through continuous use.
Accordingly, it is desirable to provide a system to perform lymphapheresis by separating the lymph into a cellular component fraction and a liquid fraction and then returning the liquid fraction to the patient. It is also desirable to have a system that includes a means for maintaining a filter in an unplugged operating condition even during prolonged use. The system of the present invention meets these desires.